1. Field of the Invention
The present invention relates to a viscous fluid type heat generating apparatus adapted for being incorporated into a vehicle heating system to be used as a heat-generating source.
2. Description of the Related Art
A viscous fluid type heat generating apparatus intended for use in a vehicle climate controlling system is disclosed in Japanese Unexamined Patent publication (Kokai) No. 10-29423 (JP-A-'423). The viscous fluid type heat generating apparatus of JP-A-'423 has a housing in which a heat-generating chamber and a heat receiving chamber, working as a water jacket and arranged adjacent to the heat-generating chamber to pass a heat exchanging fluid therethrough are formed. A drive shaft is supported to rotate via bearing devices and shaft sealing devices in the housing, and a pulley element is fixedly mounted on a front end part of the drive shaft to be rotationally driven through a belt by a vehicle engine. A rotor element is mounted on a rear end of the drive shaft to be rotatable within the heat-generating chamber. The rotor element has a pair of axially spaced fixing plates and a cylindrical outer peripheral member having opposite ends fixed to the pair of fixing plates. The heat-generating chamber has a cylindrical inner wall surface confronting the outer surface of the cylindrical outer peripheral member to define a small closed annular gap to be filled with a viscous fluid, such as silicone oil. The rotor element generates heat in the viscous fluid when rotated. The rotor element has a storing region inside the cylindrical outer peripheral member provided for storing a part of the viscous fluid without it being subjected to a shearing action applied by the rotating rotor element. The storing region fluidly communicates with the above-mentioned small heat-generating gap via withdrawal passages formed in the fixing plates. The small heat-generating gap also communicates with the storing region via fluid supply passages formed in the cylindrical outer peripheral member so that the viscous fluid can be supplied from the storing region into the heat-generating small gap.
In the described viscous fluid type heat generating apparatus as incorporated into a vehicle heating system, the rotor element rotates in the heat-generating chamber when the drive shaft is driven by the vehicle engine, and the viscous fluid in the heat-generating chamber is subjected to a shearing action within the gap between the inner wall surface of the heat-generating chamber and the outer surface of the rotor element to generate heat. The heat generated in the viscous fluid is transmitted to the heat exchanging liquid flowing through the heat receiving chamber, i.e., the water jacket, and is carried to a heat circuit by which the heat is applied to a heated area, i.e., a passenger compartment of the vehicle.
During the rotation of the rotor element, the viscous fluid is subjected to a centrifugal force by which the viscous fluid is moved from the storing region into the small annular gap via the fluid supply passages, and from the small annular gap into the storing region via the withdrawal passages. Namely, a movement of the viscous fluid occurs in the viscous fluid heat generating apparatus. Therefore, it does not occur that a specified portion of the viscous fluid is constantly subjected to the shearing action by the rotor element of the heat generating apparatus. Accordingly, thermal and mechanical degradation of the heat-generating performance of the viscous fluid can be prevented. Nevertheless, in viscous fluid type heat generating apparatus, the amount of the circulation of the viscous fluid through the small circulatory annular gap, the withdrawal passages, the storing region, and the supply passages for a unit time changes in response to a change in the rotating speed of the drive shaft and the rotor element. Thus, the heat generating apparatus might generate excessive heat when the rotor element is rotated at a very high speed, and as a result, the degradation of the heat-generating performance of the viscous fluid may occur.
More specifically, when the drive shaft is rotated at a relatively low speed to rotate the rotor element at the same low speed, the viscous fluid in the storing chamber is not subjected to any appreciable centrifugal force. Therefore, the amount of circulation of the viscous fluid through the storing region and the small annular gap generating heat is relatively small. The viscous fluid in the small annular gap is subjected to a suitable shearing action applied by the rotor element rotating at a relatively low speed. Thus, the viscous fluid generates a suitable amount of heat in the small annular gap to be effectively transmitted to the heat exchanging liquid flowing through the heat receiving chamber. Therefore, degradation in the heat-generating performance of the viscous fluid does not occur while exhibiting a desirable heat-generating performance.
On the other hand, when the drive shaft is rotated at a high speed to rotate the rotor element at the same high speed, the viscous fluid held in the storing region of the rotor element is subjected to a large centrifugal force. Therefore, a relatively large amount of the viscous fluid is circulated through the storing region and the small annular gap for heat generation, via the supply and the withdrawal passages. Accordingly, the viscous fluid is repeatedly subjected to a large shearing action and, eventually generates an excessive amount of heat. In addition, the circulation of the large amount of viscous fluid causes an imperfect heat exchanging between the viscous fluid in the small annular gap and the heat exchanging fluid in the heat receiving chamber, and thus, a heat exchanging efficiency between the heat-generating chamber and the heat receiving chamber is reduced. Therefore, degradation in the heat-generating performance of the viscous fluid might easily occur.
Further, as the rotor element of the above-describe d viscous fluid type heat generating apparatus is provided with a plurality of elements, i.e., the pair of axially spaced fixing plates and the cylindrical outer peripheral member which must be assembled together before the rotor element is mounted on the drive shaft and incorporated into the heat generating apparatus, the manufacturing cost of the rotor element must necessarily increase.